Cold cathode rectifier



Aug. 18, 1942. c. T. KNIPP i 2,293,468

COLD CATHODE RECTIFIER Filed Sept. e, 1939 2 Sheets-Sheet 2 Patente dAug. 18, 1942 4 COLD` CATHODE RECTIFIER Charles T. Knipp, Urbana, Ill.,assignor to Board of Trustees of the University of Illinois, Urbana,Ill., a corporation of Illinois Application September 16, 1939,Serial'No. %5,193

7 Claims.

The present invention relates to rectiers, particularly of theelectronic or tube type.

The invention aims primarily to provide an improved rectifiercharacterized by a cold cathode. A rectifier in which the cathodeoperates in a relatively cold state has numerous advantages overthermionic or filamentary rectifiers in which the cathode must bemaintained in a heated state by a filament or the like. For example, theburning out of the filament terminates the life of the tube much shortof the life expectancy of the other elements of the tube. Moreover, thethermal energy generated by the filament is largely dissipated as a heatloss. Furthermore, the heated electron emitting surface gradually losesits efiectiveness to emit electrons. These and other disadvantages areavoided in a cold cathode rectifier.

My improved rectifier utilizes certain of the discoveries made byCrookes and Hittorf with reference to the electrical conductivitiesprevailing within tubes which have been evacuated down to verylowkpressures, these tubes having spaced electrodes sealed thereinbetween which the electrical discharge is drawn. tablished that whenthese tubes are exhausted down to an extremely rarified or high vacuumstage, known as the Crookes' stage, and are then subjected to arelatively high voltage between the electrodes; a phenomenon in the formof a nonluminous region or dark space develops at or in immediateproximity to the electrode or electrodes which are then functioning -ascathodes. This region became known as the Crookes' dark space, andrepresents the mean free path of the issuing electrons.

Hittorfs later experiments performed on the Crookes' dark space revealedother related phenomena pertaning to increased resistance toconductivity when the Crookes' dark space is limited in its developmentor caused to envelope its respective electrode. Crookes and Hittorf didnot, however, perceive and apply the potentia1ities of the Crookes' darkspace for rectfying alternating Currents.

I have found that by controlling the Crookes' dark space of one of theelectrodes, or by establishing an unbalanced relation between theCrookes' dark spaces of different electrodes, a

Very effective rectifying action can be obtained without the employmentof a heated cathode or other thermionic agency. This improved coldcathode rectifier comprises a tube or like chamber enclosing a pluralityof electrodes preferably Crookes esshroud or equivalent element whichlimits the development of the Crookes' dark space or approximatelyencloses this dark space at that electrode. At the Crookes' stage ofevacuation of the tube, this barrier or hood prevents that electrodefrom functioning as a cathode, so that it thereafter functons solely asan anode, for producing the desired unilateral conductivty.

One manner in which my invention may be carried into efiect isillustrated in the accompanying drawings illustrating different specificembodiments of the tube. In such drawings:

Figure 1 is a longitudinal sectional view of one embodiment -employingthree electrodes for obtaining full-wave rectification;

Figure 2 is a simple circut diagram illustrating one typical use of thetube; and

Figures 3, 4 and 5 are longitudinal sectional views illustrating otherembodiments of the tube.

Referring to Figure 1, the body of the tube ll) is shown as beingcomposed of glass, although it will be understood that it may becomposed of other insulating materials, or might even be made of ametal. The electrodes ll, !2 and !3 preferably consist of aluminum rodsfused in position in glass seals M, !5 and !6 respectively. The outerends of the rods carry any suitable connector terminals I'l, !8, and efor making connection with the circuit. The two electrodes l2 and |3shown as disposed in the lower part of the tube are arranged to functionsolely as anodes, in consequence of which the electrode H shown in theupper part of the tube is caused to function solely as a cathode. Thetwo lower electrodes are made to function solely as ancdes by the em--ployment of the above mentioned barriers or hoods in association withsaid lower electrodes. In the exemplary Construction illustrated inFgure 1, these take the form of cylindrical glass hoods or envelopes !2'and IS' which substantially enclose the electrodes !2 and 13, in spacedrelation thereto. The two hoods are preferably substantially identical,the cylindrcal inner walls of each being spaced substantially uniformlyfrom the cylindrical outer surfaces of their respective electrodes. Theclosed inner ends of said hoods are also preferably spaced from theconsisting of `plain metallic rods or other simple inner ends of theirelectrodes. The open outer end of each hood preierably extends beyondthe bare metal surface of its respective electrode to overlie a portionof the glass seal !5, IG. Any suitable supporting struts, spiders orlike arrangement may be employed for supporting the hoods 12', 13' inthe above relation to their respective electrodes. In one typicalembodiment of the invention, each of the electrodes consists of analuminum rod of approximately millimeters in diameter, and the radialdistance from the surface of such electrode to the irmer walls of itsrespective hood is approximately 2 centimeters. I wish it to beunderstood, of course, that the above described arrangements andproportions are merely illustrative and not limitatve.

The tube may be evacuated to the desired clegree by connection with amercury pump or the like, following which the tube may be permanentlyclosed by a hermetic seal. As alternative procedures, the tube mayremain connected with the mercury pump or other exhausting means forintermittent or continuous exhausting during operation; or, after beingthus exhausted by the pump, the tube may remain connected with areceptacle formed as a part of the tube and containing charcoal, thischarcoal being adapted to absorb gas from the tube when the charcoal iscooled by the action of liquid air or the like. The embodiment shown inFigure 1 illustrates such a receptacle 22 joined to the rectifier H) bythe connecting neck portion 23 and containing a mass of charcoal 24. Avessel containing licuid air can be brought up to immerse the receptacleor bulb 22 in the liquid air, thereby bringing the temperature of thecharcoal down to a very low point, which results in the charcoalefiectively absorbing gas remaining in the tube. If desired, a stop-cockor the like may be interposed in the connecting neck portion 23, so asto enable the bulb receptacle 22 to be disconnected from the rectifiertube for maintainin the pressure substantially constant in the tubeover`1ong periods of time. The Crookes' stage of rarefaction at whichsatisfactory rectifying action occurs is a vacuum in the ne-ighborhoodof .001 mm. Hg or less.

Typical circuit connections for full-Wave rectification are illustratedin Figure 2. Any suitable transformer 26, or connected pair of transvformers, establishing a center tap or split secondary 27, may beemployed for supplying the potential to the rectifying tube. The endterminals of the secondary 21 are connected to the two anode electrodes!2 and !3 of the tube. The center tap of the secondary is connected toone side of the direct current load L, and the cathode electrode ll ofthe tube is connected to the other side of the load L. This load mightbe an X-ray tube, a Geissler tube, or any other' direct current device,preferably of high potential characteristic. In the Geissler tubeillustrated, the anode is indicated at 3i and the cathode at 32. Typicalalternating current Voltages which have been rectied in the rectifyingtube lil have ranged from 5000 to 25,000 volts, but it will beunderstood that higher or lower voltage ranges may be employed,depending upon the dimensions of the rectifying tube, etc.

In the operation oi the tube, the existence of a relatively low pressurewithin the tube is appare-ntly an important factor for securing thedesired rectication. For example, if the tube is subjected to itsOperating potential When it has only been exhausted down approximatelyto the Geissler stage (approximately .05 mm. Hg) the alternatingdischarge passes back and forth between the electrodes about equallywell in both directions, the electrodes serving alternately as cathodeand anode. In other words, at these gas pressures the glass barrier orhood exerts little or no rectifying action. However, if the vacuum inthe rectifying tube is now made higher as by the cl-arcoal-in-liquid-aircontrol) until the Crockes' dark space (i. e., the mean free path of theissuing electrons) reaches to or extends beyond the inside 'chmensionsof the glass hoods l2' and l', then the respective electrodes !2 and [3can no longer function as cathodes, i. e., they serve as anodes only.The discharge through the tube is now unidirectonal, the cut-off beingvery sharp at the neutral line, With no fringing or feathering outvisible in cathode-ray oscillographs. The opening of either one of thetwo switches 28 or 29 leading to the two anodes !2 and !3 giveshalf-wave rectification, and this half-wave rectification likewise seemsto be perfect, with no fringing or feathering out Visible, and therectification on one alternation being substantially identical ,with therectication on the other alternation. Of course, where halfwaverectification is to be performed continuously, a two electrode tube isemployed, as hereinafter described. The abruptness with which therectiiying action starts as the gas pressure in the tube is lowered tothe Crooke-s' stage depends on the geometrical accuracy of the hood orhoods l2'-l3'; The radial distance from the surface of each electrodel2-l3 to its glass envelope l2'--l3' should be uniform at all points.such electrons as are projected from the electrodes I 2-l3 leave thesurfaces of said electrodes in directions normal or at right angles tosaid suraces, and it is important that these electrons must not get outof the hoods |2'-l3'. Accordingly, the open ends of these hoods arearranged to extend to or overlie a portion of the glass seal !5-16 ateach of said anode electrodes.

Figure 3-il1ustrates another construction of three electrode tube forfull-wave rectification.

The two anodes Iza and lsa. enter the tube lo in diametrically oppositerelation. The exposed portions of these electrodes extend into a glasscylinder 34, which has a transverse diaphragm or partition 35 of glassor other insulating material disposed in the cylinder 34 intermediateits ends. The resulting structure constitutes a hood for each of theanodes Iza-Isa. This cylindrical hood structure may be mounted by anysuitable supporting posts, spider arms or the like, as previouslydescribed. surrounding said glass cylinder is the cathode l la, thisbeing in the form of a metallic ring which is spaced circumferentiallyfrom the glass sleeve 34 and is disposed equidistant from the oppositeends thereof. A suitable Connector terminal I'la extends from thecathode ring Ha outwardly through a glass seal l4a. The same evacuatingmethods and apparatus may be employed in connection with this tube aswere previously described. The operation of the tube is also the same aspreviously described.

Figure 4 illustrates a simple form of two electrode tube for effectinghalf-wave rectication The construction and operation of this tube willbe apparent from the preceding description.

Figure 5 illustrates another embodiment of two electrode tube in which amodified construction of hood is employed. This hood structure comprisesan insulating sleeve portion 38 spaced radially from its associatedelectrode, a second insulating sleeve portion 39 likewise spacedradially from the electrode, and an oute' hood 40 which envelopes bothsleeve portions 38 and 39. These three portions 38, 39 and 40 may beconstructed of glass or any other suitable insuiating material. The openspace 4! is preferably in the form of a continuous annular gap betweenthe adjacent ends of the sleeve portions 38 and 39, although, as amodified arrangement, these two sleeve portions may be in the form of acontinuous sleeve structure formed with spaced holes 4| located atdifferent points around the sleeve. Where the sleeve portions areseparate, the outer sleeve portion 39 and hood 49 can be supported bymounting posts, spider arms or in any other suitable way. The outer hoodta intercepts electrons emitted radially out through the space oropenings 41.

While I have illustrated and described what I regard to be the preferredembodiments of my invention, nevertheless it will be understood thatsuch are merely exemplary and that numerous modications andrearrangements may be made therein without departing from the essence ofthe invention.

I claim:

l. A full-wave cold cathode rectifier comprising a tube having a gaspressure of the order of .001 mm. of mercury, three electrodes extendingsubstantially radially into said tube from different angles, andinsulating hoods enveloping two of said electrodes for causing saidlatter electrodes to function solely as anodes, the inner ends of saidhoods adjacent to the third electrode being closed and the outer ends ofsaid hoods being open.

2. A cold cathode rectier comprising a tube having a gas pressure of theorder of .001 mm. of mercury, a plurality of electrodes extendingsubstantially radially into said tube from different angles, and aninsulating hood enveloping one of said electrodes for causing saidlatte' electrode to function solely as an anode, the inner end of saidhood adjacent another of said electrodes being closed, and the other endof said hood being open.

3. A cold cathode rectifier comprising a tube having a gas pressure ofthe order of .(301 mm. of mercury, a pair of electrodes extending intosaid tube from different angles, and an insulating hood enveloping on ofsaid electrodes for causing said latter electrode to function solely asan anode, the inner end of said hood adjacent the other of saidelectrodes being closed, and the outer end of said hood being open.

4. A full-wave cold cathode rectier conp'ising a tube having a gaspressure of the order of .001 mm. of mercury, three electrodes extendingsubstantially radially into said tube from different angles, and conningstructures ccmposed of insulatng material partially enveloping two ofsaid electrodes for causing said latter electrodes to function solely asanodes, the third electrode :being adapted to function as a cathode,said confining structures comprising end hoods and also comprisingopenings disposed outwardly of said end hoods, said hoods beinginterposed as barriers between the inner ends of their respective anodesand the inner end of said cathode, said openings permitting electrons toflow from said cathode to said anodes but preventing electrcns emittedby said anodes from having any straight line path of flow from saidanodes to said cathode.

5 A cold cathode 'ectifier comprising a tube having a gas pressure ofthe order of .001 mm. of mercury, a plurality of electrodes extendinginto said tube from different angles, and a confining structure composedof insulating material partiaily enveloping one of said electrodes forcausing said latter electrode to function solely as an anode, another ofsaid electrodes being adapted to function as a cathode, said confinngstructure comprising an end hood and also comprising an opening disposedoutwardly of said end hood, said hood being interposed as a barrierbetween the inner end of its respective anode and the inner end of saidcathode, said opening permitting electrons to flow from said cathode tosaid anode, -but preventing electrons issuing from said anode fromhaving any straight line path of flow from said anode to said cathode.

6. An electron device for utilizing Crookes' dark space phenomena toeffect cold cathode rectication of alternating Currents, comprising anenvelope evacuated to the Crookes' stage of evacuation approximately ofthe order of .001

of rne'cury, a plurality of electrodes extending into said chamber andadapted for connection with an alternating current circuit of sufiicientpotential to create a crookes dark space at each electrode, andinsulating hood means housing one of said electrodes for confining thedevelopment of the Crookes' dark space at said latter electrode and themean free path of the electrons issuing therefrom, whereby said latterelectrode is caused to function solely as an anode.

7. An electron device 'for utilizing Crookes' dark space phenomena toefiect cold cathode rectification of alternating Currents, comprising anenvelope evacuated to the Crookes' stage of evacuaton approximately ofthe order of .001 mm. of mercury, a plurality of electrodes in saidCham-ber adapted to be energized by an alternating current of sufiicientpotential to create a Crookes' dark space at each electrode, and barriermeans of insulating material housing one of said electrodes forconfining the mean free path of the electrons issuing therefrom, wherebysaid latter electrode is caused to function solely as an anode, andanother of said electrodes is enabled to function as a cold cathode.

CHARLES T. KNIPP.

